Guided wave testing is developing as a method of nondestructive evaluation (NDE) of anomalies in structural components. Such anomalies include the development and spread of corrosion, cracks, voids, and other defects incurred due to environmental stressors such as corrosive materials, stresses associated with use including thermal or mechanical fatigue, or discrete events such as seismic events. Guided waves may be generated directly in a component or coupled to a component using an actuator to impart ultrasonic vibrations. Guided wave testing has been used to monitor pipelines, plates, aircraft structures, bridge cables, and heat exchanger tubing.
Sensors for use in guided wave monitoring may be located adjacent to component walls or surfaces. However, thermal expansion and chemical changes, such as corrosion, may reduce the coupling between the sensors and the component surfaces. For example, pipe or hose clamps used to hold sensors in place may expand in elevated temperature conditions and fail to retain their shape, reducing the effectiveness of the coupling between the sensors and component wall surfaces. Spring loaded pipe clamps using flat or wave springs and Belleville washers exhibit relatively high profiles making it difficult to deploy the sensors in crowded areas. For example, a sensor may have a thickness about 0.125 inches, and the clamp loaded with wave springs on top of the sensor may add another inch or more. However, a gap between adjacent pipes on the order of 0.25 inches is not uncommon, leaving little room to accommodate the sensors. In addition, a clamp mounted on top of a sensor is difficult to adjust on a pipe when additional heating pipes are mounded parallel to the pipe body. In this case, the clamping ring would be positioned over the heating tubes, which may have a diameter of up to two or three inches. This may cause the set up to be bulky and expensive.
Further, flat springs, wave springs, and Belleville washers are either limited to grades of steel that typically do not operate at 500° C. or are not corrosion resistant. Thermal expansion and environmental stresses may also cause delamination of adhesives used to couple sensors to walls. Furthermore, corrosion of coupling elements may reduce coupling between sensors and components. Accordingly, there remains a need to improve the coupling of sensors to component walls and devices used therefore.